1. Field of the Invention
The present invention relates to an electrodeposition resinous paint composition suitably employable as a resist for the formation of a through-hole and a circuit pattern in a circuit-printed board having a through-hole.
2. Description of Prior Art
As electrodeposition resinous paints (i.e., resinous paints for electrical deposition), there are known an anionic paint and a cationic paint. The anionic paint can be obtained by neutralizing a maleic oil synthesized from a natural drying oil and maleic anhydride, a phenol modified maleic oil obtained by modifying said maleic oil with a phenol resin, a resin such as a copolymer of an acrylic acid or its ester, or a modified alkyd resin prepared by esterifying a polybasic acid and a polyhydric alcohol, with an amine, a potassium hydorxide or the like to make it water-soluble or water-dispersible. The cationic paint can be prepared by reacting an epoxy resin with a secondary amine to cleave at least a portion of epoxy groups in the epoxy resin and neutralizing the resulting resin to make it water-soluble or water-dispersible.
The present inventors have already developed a process for the preparation of a circuit-printed board having a through-hole using an electrodeposition resinous paint as a resist for forming a through-hole and a circuit pattern.
The steps of the process can be schematically described by referring to FIG. 1 of the attached drawings.
In the first step, a board 1 (substrate) laminated with a copper foil on both surfaces and having a through-hole 2 is plated to form a plated layer 3 on the substrate, as shown in (1) of FIG. 1. In the second step, a resist layer 4 having a reverse pattern for a desired circuit pattern is formed on the surface of the plated layer 3 on the substrate 1, as shown in (2) of FIG. 1. Subsequently, on the exposed area of the plated layer 3 was deposited a resinous paint layer 5 by electrical deposition, as shown in (3) of FIG. 1. Thereafter, only the resist layer is removed as shown in (4) of FIG. 1, and then the exposed portion of the plated layer and the copper foil placed thereunder are removed by etching as shown in (5) of FIG. 1. Finally, the deposited resinous layer 5 is removed as shown in (6) of FIG. 1, to prepare a circuit-printed board having a through-hole.
The above-described process can be employable to efficiently prepare a circuit-printed board having a through-hole with high productivity. However, this process has various drawbacks in the case of using the aforementioned conventional resinous paints as a material of the deposited resinous paint layer.
For example, the conventional resinous paints except the paint of modified alkyd resin should be subjected to a heat treatment at a high temperature in the range of 180.degree. to 200.degree. C. to obtain high resistance required for the etching stage. Under the conditions of such heat treatment, curing of the resist layer having the reverse pattern is accelerated, whereby it is made difficult to remove only the resist layer and further it is also difficult to remove the deposited resinous paint layer at a later step.
A resinous paint of the modified alkyd resin can be cured by a heat treatment at a low temperature such as approx. 130.degree. C. and has a resistance to etching. However, in the case of forming a pattern of extremely small size such as a pattern of approx. 100 .mu.m wide, the deposited resinous paint layer tends to be removed with the resist layer in the stage of removing the resist layer.
It is desired that a resinous paint layer having uniform thickness is formed on the wall of the through-hole in the manner as shown in FIG. 2. However, if the conventional resinous paint is electrically deposited over the wall of the through-hole, the deposited layer is easily softened to flow down from the edge portion of the through-hole because of surface tension, etc. in the heat subsequent treatment procedure, as shown in FIG. 3, whereby the plated layer is apt to be etched out at the edge portion of the through-hole by an etching solution in the etching stage.
Further, the deposited layer of the aforementioned conventional resinous paint generally has a low surface hardness, and hence the layer is liable to be damaged in contact with a roll, etc. in the conveying procedure applied to the board.